Polyolefin waxes, in particular polyethylene waxes, are widely used as formulation components for the preparation of solvent-containing pastes for use, for example, in the care of floorings, automobiles and shoes (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A 28, pages 108, 153, 156, Weinheim 1996). Wax pastes are formed by allowing hot wax solutions in organic solvents to cool. The paste form enables easy application of the waxes: after mechanical spreading of the paste on the surface to be treated, the solvent evaporates and a protective, preserving or otherwise active wax film remains.
For formulation of pastes comprising polyolefin wax, further waxes, such as, for example, block paraffins, microwaxes and refined carnauba or partly hydrolyzed and/or nonhydrolyzed montan waxes, and furthermore auxiliaries for fine adjustment, such as metal stearates, are as a rule employed. Hydrocarbons, such as, for example, aromatic-containing or aromatic-free benzines or turpentine oil, are usually used as the solvent.
A quality-determining property of such pastes is, in addition to the nature of the surface (gloss) and heat stability, their consistency (in this context cf.: Seifen-Ole-Fette-Wachse, No. 20/1957, page 595). The measurement parameter for the latter is as a rule the so-called paste hardeners, with which the stability of the paste body is determined. The quality criterion here is the paste hardness both of the pure wax ("solvent uptake") and of mixtures formulated in practice with further wax components which form pastes less readily ("paste-forming capacity"). The dependence of the paste hardness on the temperature and storage time is also of decisive importance for the evaluation.
Polyolefin wax components which are used in the formulation of pastes are primarily polyethylene waxes, in particular those which contain side chain branchings. Such waxes can be prepared by thermal degradation of branched highly polymeric polyethylene plastics or by direct polymerization of ethylene. Possible polymerization processes are, for example, high pressure technologies, in which ethylene is converted by free radicals at high pressures and temperatures into branched waxes, and in addition low pressure or Ziegler processes, in which ethylene is polymerized with the aid of organometallic catalysts at comparatively low pressures and temperatures. If the low pressure process is used, the branchings are as a rule introduced into the polyethylene chain by copolymerization of the ethylene with larger or smaller proportions of longer-chain olefin monomers, for example propene or 1-butene.
A procedure in which metallocene compounds are used as organometallic catalysts has recently been disclosed as a variant of the low pressure process. These compounds comprise atoms of titanium, zirconium or hafnium as the active species and are as a rule employed in combination with cocatalysts, for example organoaluminum or boron compounds, preferably aluminoxane compounds. If required, the polymerization is carried out in the presence of hydrogen as a molecular weight regulator. Metallocene processes are distinguished by the fact that waxes having a narrower molecular weight distribution, more uniform incorporation of comonomers, lower melting points and higher catalyst yields can be obtained compared with the older Ziegler technology.
Corresponding polymerization processes for the preparation of polyolefin waxes which operate with metallocene catalysts are described, for example, in EP-A-571882.